When we only want one result per transaction, that means we only want the Body, or Main Line, of each transaction. To accomplish this, there is a filter named "Main Line".
By setting the Main Line filter to Yes in our search criteria, we are essentially saying "Only show me body-level data for the transactions in my results":
Modifying our previous search criteria this way now gives us the single result we expected originally:
If we reverse our Main Line filter to No, we are saying "Show me only the data from sublists in my results":
To recap Main Line's behaviour:
Note that the Main Line filter is not supported for Journal Entry searches.